Diabolo – A failed OLTC Experiment

After Playing with my
AD-OLTC for a while it was time for something a little different.

My thoughts ran somthing like, "If I can double the bus voltage I can quadruple the bang energy for the same current." So I re-designed the AD-OLTC to use IGBT's in series to give me a bus voltage of 1.6Kv max

Secondary: 666T of 0.22mm enamelled copper wire on a 100mm diameter PVC former 500mm Tall.
Primary: 2T 5mm copper pipe.
Topload: 12" Stainless ball
Primary Cap: 1.41uF (12x0.47uF @1kV 6 strings of two)
Transistors: 4 x 4PF50WD. (two banks of two in series)


The primary circuit has everything that an OLTC usually has, but doubled. fed into a single primary coil. The whole lot is mounted onto a single peice of double sided copper clad, hopefully to keep the stray inductance down. The pairs of IGBT's and capacitors are effectivly in series, giving me 2Kv of capacitors and 1.8Kv max across the IGBT's. Leaving some head room for spikes, this gives me 1.6Kv switched. There are two 400V tranzorbs across each IGBT to catch the transients. The charging choke is 2.5mH, made from a whole real of 1.25mm enammeled wire.
The drive of course needs to be split into two isolated drives. Each drive has its own mains transformer, rectifier, and tl250 opto driver. These two optosare driven from a single monostable timing circuit, which is in turn triggered optically from the controller.
So far in fairly low voltage tests I have got 5" streamers to air. The whole system needs tuning thoroughly before I up the voltage. At the moment the IGBT''s appear to be sharing the voltage equally and I dont get any sharp switching spikes from uneven drive signals.